Selenium rectifier having light metal carrier electrodes



Oct.- 10, 1939. F. BRUNKE El AL 2,175,873

SELENIUM RECTIFIER HAVING LIGKT METAL C ARRIER ELECTRODES Filed Oct. 2a, 1938 COUNTER ELECTRODE. 6 BLOCKING LAYER.

SELENIUM CARBON. OXIDE AND CARBON. METAL OR METAL ALLOY OF THE GROUP CONSISTING OF ALUMINUM, MAGNESIUM ANUBERYLLIUH- Inventors: Fritz Brun ke, Werner Koch,

Their Attorney.

- trode layer.

Patented on. 10, 1939 UNITED STATES PATENT OFFICE METAL CARRIE Fritz Brunke, Reinicken Berlin-Giienicke,

R ELECTRODES dorf, and Werner Koch,

Germany, assignors to General Electric Company, a corporation of New York Application October 28,

In G

1938, Serial No. 237,540

ermany November 12, 1937 6 Claims. (01. 175-366) Our invention relates to dry plate rectifiers and like devices such as light sensitive cells, of the type having a light metal as the carrier or base electrode, and particularly to an improved method of producing selenium rectifiers and like devices having a light metal as the base electrode.

Dlfliculties have been encountered in the attempt to manufacture selenium rectifiers and like devices having carrier electrodes of light metal such as magnesium, aluminum or beryllium. It has been found that when employing conventional methods of applying the selenium to the carrier electrode a blocking layer develops between the carrier electrode and the selenium due to the oxide film with which the light metal is normally covered.

In application, Serial No. 147,104, filed June 8, 1937, and assigned to the same assignee as the present application, a process is described whereby these difliculties are overcome. In accordance with this process, in the manufacture of dry rectifiers of the selenium type and having a light metal carrier electrode a finely divided metal is deposited on and penetrates into the oxide layer, For this purpose the carrier electrode is exposed for a short time in a vaccum to an atomized or vaporized jet of the metal. The blocking action of the carrier electrode oxide layer is therefore prevented by reason of the conductivity imparted to the layer by the finely divided metal.

It is the principal object of the present invention to provide an especially simple process for the manufacture of selenium type rectifiers having conductive material deposited on the carrier elec- We have found that carbon is particularly well suited for use as the deposit of conductive material on and in the oxide layer, the carbon deposit acting like a metal on account of the relatively high conductivity of carbon. Instead, therefore, of employing a vaporized or atomized metal as described in the prior application, in accordance with the present invention carbon is employed for the deposit.

It is already'known to employ carbon as material for the base or carrier electrode of the semi-conductive or selenum layer, and also to employ carbon as material for an intermediate layer between the carrier electrode and the selenium layer, In these prior known rectifiers, however, the carbon layer is in the form of a relatively thick sheet which either is self-supporting, or if in the form of a sheet which is applied to a metal carrier electrode, is of such thickness that it effectually prevents any chemical combining of the selenium with the carrier electrode metal. Therefore, in the prior selenium rectifier employing a carbon layer on the carrier element the metal of the latter element does not function chemically as an electrode but only as which mechanically supports the ,5

carbon has an entirely different purpose from that of the carbon layer or sheet above mentioned as known to the prior art, since in the present invention the carbon deposit serves to prevent the blocking action on the light metal carrier electrode, without in general altering the character of the latter electrode. Accordingly, the carbon deposit may be, and preferably is, extremely thin so that the action of the carrier electrode metal on the semiconducting layer is not afi'ected. Consequently, the carbon is merely embedded in, the oxide film with usually a small excess of carbon on the surface of the film, in the same manner as in the process described in the above mentioned prior application wherein finely divided metal penetrates into the oxide film to render the latter conductive. The upper limit of thickness of the layers comprising the oxide film having the carbon embedded therein, together with the excess of carbon which may be present, is determined by forming the layer of such thickness that the carbon is just discernible, without showing colors due to light interference. This layer may preferably be of 10- mm. total thickness at the most.

The depositin of the carbon may be accomplished by a vaporization process similar to that described in'the above mentioned prior application, but may also be accomplished in any other suitable manner which permits the deposit of the carbon particles in the order of magnitude of atoms. If, for example, electrically charged particles are employed, the force of the impact of the particles may be considerably increased by the provision of accelerating fields and thus the embedding of the carbon particles in the oxide film may be facilitated, As a criterion in determining whether the carbon is satisfactorily embedded in or applied to the carrier electrode the test may be used which consists in determining whether the undesirable blocking action due to the carrier electrode oxide film is avoided when the layer, constituted by the oxide having carbon deposited therein and any excess of carbon, is of the above mentioned order of thickness.

of the surface layer of oxide The novel features which are considered to be characteristic of our invention are set forth with particularity in the appended claims. Our invention itself. however, both as to its organization and method of operation together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing the sinsle figure of which is a crosssectional view of a selenium rectifier cell or element having a light metal base or carrier electrode treated in accordance with the method of the present invention.

In the figure of the drawing the rectifier or the like cell or element comprises a base or carrier electrode i of a light metal, for example, of the group including aluminum, magnesium and beryllium or an alloy of metals of this group. The electrode I may be, for example, a magnesium sheet 1 mm. in thickness. The carbon is deposited on the oxide film of the magnesium sheet I, the carbon penetrating the oxide to form the conductive layer 2. Any slight excess of the carbon particles form a thin carbon layer 3 upon the oxide and carbon layer 2. The numeral 4 designates the semi-conducting layer formed in the present case of selenium, which may be applied in the molten condition and which may have a thicknes of the order of 0.10 mm. Any other usual processmay be employed for the applying of the semi-conducting layer 4. On the blocking layer 5 is counter electrode 0 which may be formed of Wood's metal by the sputtering process.

In applying the carbon to the oxide film of carrier electrode I, while an excess of the carbon facilitates the production. on the carrier electrode I, of a film which is suitably conductive, this excess is not necessary. The depositing only of carbon particles substantially all of which become embedded in the surface of the carrier electrode oxide film is sufficient. Further, for the semiconducting layer 4 any layer of the selenium type may be employed, i. e., any semi-conducting layer which carries the blocking layer 5 on the side thereof which is opposite the carrier electrode i.

The depositing of the carbon on the carrier electrode oxide film may be accomplished by placing the carrier electrode in the vicinity of a car bon arc, and at a distance of a few centimeters therefrom, which is burning under reduced pressure, approximately 1 mm., preferably in a rare gas atmosphere. The period of exposure of the carrier electrode to the arc is of the order of a a few seconds, the time of exposure not being long enough to cause any coloration of the film, due to light interference, to become visible.

Our invention has beendisclosed herein in a particular embodiment for purposes of illustra- .tion. It is to be understood, however, that the invention is susceptible of various changes and modifications and that by the appended claims we intend to cover any such modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. The method of producing dry plate elements of the selenium type which includes providing a carrier electrode composed of a light metal having an oxide film thereon, applying a plurality of particles of finely divided carbon to the surface of said film, applying a layer comprising selenium to said surface having said carbon applied thereto, and applying a counter electrode to said layer, the amount of said carbon being so limited that said light metal acts chemically with said selenium layer.

2. The method of producing dry plate elements of the selenium type which includes providing a carrier electrode composed of a material of the group comprising aluminum. magnesium and beryllium and alloys of said. metals. said electrode having an oxide film thereon, applying a thin layer of finely divided carbon to said film, applying a layer comprising selenium to said firstnamed layer, and applying a counter electrode to said last-named layer, the thickness of said carbon layer being such that said carrier electrode acts chemically with said layer comprising selenium layer.

3. The method of producing dry plate elements of the selenium type which includes providing a carrier electrode composed of a light metal having an oxide film thereon, applying finely divided carbon to the surface of said film to produce a layer constituted by said film having particles of said carbon embedded therein and a thin layer of said carbon thereon, the total thickness of said layer not exceeding substantially 10- mm., applying a layer comprising selenium to said firstnamed layer, and applying a counter electrode to said second-named layer.

' 4. The method of producing dry plate elements of the selenium type which includes providing a carrier electrode composed of a light metal having an oxide film thereon. exposing said film to a carbon-arc burning under a relatively low pres sure in a rare gas atmosphere thereby to deposit carbon in the surface of said film, applying a layer comprising selenium to said film, and applying a counter electrode to said layer.

5. A dry plate element including a carrier electrode composed of a light metal having an oxide film thereon, a plurality of particles of finely divided carbon embedded in the surface of said film, a semi-conductive layer comprising selenium in contact with said surface of said film, and a counter electrode in cont-act with said semi-com ductive layer.

6. A dry plate element including a carrier electrode composed of a light metal having an oxide film thereon, a plurality of particles of finely divided carbon embedded in the surface of said film, a thin layer of finely divided carbon in contact with said surface of said film, a semi-conductive layer comprising selenium in contact with said carbon layer, and a. counter electrode in contact with said semi-conductive layer.

FRITZ BRUNKE. WERNER KOCH. 

